We have mentioned above that Carrollian structures emerge naturally on all null surfaces. The event horizons of generic black holes form an important class of these null surfaces and defining theories on these null surfaces naturally gives rise of Carrollian (conformal) field theories. The emergence of Carrollian and BMS symmetries (as well as “BMS-like" symmetries) on black hole even horizons have been addressed in [1]}, [2]}, [3]}, [4]}, [5]}, [6]}. If one wishes to define quantum field theories living on black hole event horizons, it is but natural that these theories would imbibe the Carroll structures that appear geometrically on these degenerate backgrounds. The investigation of Carrollian field theories become important in this context as well.
